The MPU gives all seven flashes but none of the displays light.

All score displays blank with the MPU fully booting

Cause: Usually no high voltage: rectifier board F2 or its 1N4004 rectifier diodes, the SDB HV fuse, the regulator, or the J3 connector. Less often a stuck blanking signal, a faulty sound board, or every glass outgassed.

Checks

• Check rectifier board F2 (3/4 A slow-blow) and TP2 for about 230 V DC; if F2 is blown and TP2 is dead, test the four 1N4004 diodes in circuit.
• Check the solenoid driver HV fuse (3/16 A). If it is blown, look for a short on a display or the harness.
• Measure SDB TP2 for 170-190 V, then SDB J3 pin 8 for that voltage leaving the board.
• At each display, J1 pin 1 should have the high voltage and J1 pin 20 +5 V; display test points are TP1 +5 V, TP2 170-190 V, TP3 ground.
• If voltages are present, unplug every connector from the sound board and retest (page 56).

Fix

• Replace the failed fuse, diodes or connector pins, rebuild the HV section, or repair the sound board.

The solenoid driver / regulator board makes about 190 V DC for the score displays (around 230 V on some Stern boards); a shock from it hurts. Work with the game unplugged and let the filter capacitors discharge, and use one hand and insulated probes for live checks.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• No score displays light at all
• Score display J1 to MPU J1 connections
• Score displays dim
• One or two score displays completely blank
• Flickering score displays
• A display not working from MPU or sound board faults
• Replace a score display glass
• Bally and Stern score display boards

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)